This project is designed to examine human neoplastic cells for the presence of nucleotide sequences that may be related to those of RNA genomes of mammalian RNA tumor viruses using molecular hybridization techniques. A competition hybridization assay has been developed and employed to elucidate nucleotide sequence relations of selected mammalian RNA tumor viruses. The results of these experiments confirm and extend our previous findings that murine RNA tumor viruses can be divided into four distinct virus subgroups. In other studies, three human sarcoma cell cultures and one human lymphoma cell culture have been found to release particulate components containing high-molecular-weight RNA species characteristic of RNA genomes of RNA tumor viruses. The results of cross-hybridization experiments indicate that the high-molecular-weight RNA species released by these human neoplastic cell cultures share nucletoide sequences with viral DNA transcripts of sarcoma viruses, but not with those of leukemia or endogenous viruses. BIBLIOGRAPHIC REFERENCES: Chan, J.C., J.L. East, and L. Dmochowski. 1975. Sarcoma-negative leukemia-positive transformed cell culture established from murine sarcoma virus-induced rat bone tumor. Cancer Res. 35: 2475-2481. East, J.L., J.E. Knesek, J.C. Chan, K. Maruyama, E.S. Priori, and L. Dmochowski. 1976. Sequence relatedness of mammalian viral RNA genomes and RNA species released by human neoplastic cells. Bibl. Haemat. 43:484-487.